This invention relates to imaging systems using electronic detectors, such as charge-coupled devices (CCDs).
CCDs containing multi-pixel arrays are typically used in imaging systems to detect optical radiation and generate electronic images. When exposed to an optical field, each pixel in the array generates a light-induced electronic charge related to the intensity of the field. The charges of the array are then digitized and processed to generate the resultant digital image. Image resolution is dictated by the parameters of the CCD's pixel array; current high-end CCDs typically include 2048.times.2048-pixel arrays having dimensions of about 5 cm.times.5 cm, with each pixel having a dimension of about 25 .mu.m.times.25 .mu.m. CCDs having high spatial resolution are particularly useful, for example, in fields such as mammography and radiography, where sizes of the smallest lesions are typically between about 0.2 and 0.4 mm.sup.2.
While CCDs represent effective means for generating digital electronic images, they are expensive and have limited spatial resolution and detector area. In particular, CCDs fabricated to detect large-area images with high spatial resolution are prohibitively expensive as the cost of a CCD scales non-linearly with the size of the pixel array. Moreover, the probability of defects within the pixel array is greatly increased for large-area CCDs. Lower-cost CCDs with adequate spatial resolution are commercially available, although the detector areas of these devices are often too small to effectively image a region of interest.
There is a need, therefore, to generate detection methods and devices for producing large-area, high-resolution images at reasonable costs. Imaging techniques involving the combination of images detected with multiple CCDs, each having high spatial resolution but a small effective area, have been taught in the prior art. For instance, U.S. Pat. No. 5,138,642 describes an X-ray system that generates multiple segments of an optical image; each segment is delivered to a separate CCD detector. The light-induced signals from each detector are then combined to produce an image containing each of the segments.